stabilizing ester-plasticizers



Sept. 3, 1957 Filed Sept. 19, 1955 P. BOURGUIGNON ETAL STABILIZING ESTERPLASTICIZERS 2 Sheeis-Sheet 1 INVENTORS. P1 EERE BOUEGU/GNON.

B4 UL BIA RNA ls. BY

A TTORNEKS.

Sept- 1957 P. BOURGUIGNON EIAL 2,805,246

STABILIZING ESTER PLASTIQIZERS Filed Sept. 19, 1955 I N V EN TORS H see:Bouec'u/ GNON.

PA 01. BIA ENA IS. BY

" 2 Sheets-5116,51. 2

.ing to the test). Another test appearing in 'strong acid inactive.above, a dialkyl sulfate or similar alkyl compound with United StatesPatent *O STABILIZIN G ESTER 'PLASTICIZERS Pierre Bourguignon and PaulBiarnais, MelleyFrance, as-

signors to Les Usines d-e Melle (Societe Anonyme),

This invention relates to the purification of ester plasticizers whichcontain a strong acid radical derived from sulfuric or other strongacids.

Ester plasticizers for use with synthetic resins must withstand heattreatment during the manufacture of articles therefrom. Heatinggenerally alters ester plasticizers and heated mixtures of suchplasticizers with synthetic resins tend to darken or otherwise changecolor and to become acid. Heat stability tests for such plasticizershave, therefore, been established by manufacturers. Such tests are basedupon determination of acidity and color developed by heating theplasticizer for a given time at a high temperature (usually 160-200 C.accord- Analytical Chemistry published by The American Chemical Society,Easton, Pa, November 4, 1951, page 1692, requires heating of theplasticizer for a given time at high temperature with a piece offilter-paper immersed therein. The degree of discoloration of thefilter-paper on such heating indicates the heat instability of theplasticizer.

Most plasticizers are esters and are produced by esterification in thepresence of a strong acid catalyst such as sulfuric acid or sulfonicacids. After the continous or batch production of the ester,neutralization and other treatments thereof, such as washing, there isusually obtained an ester plasticizer meeting any and 1all equirementsas to color and physical and chemical characteristics, but whose heatstability is low. On heating at a high temperature such as mentionedabove, such material with a low heat stability, strong color and aciditydevelop therein. When such low stability material is tested with thefilter-paper test, the filter-paper becomes dark colored.

The principle object of the invention accordingly is to provide a simpleand efiicient process for improving the heat stability of suchplasticizers and to provide a sat-isfactorily stabilized product. Theinvention accordingly comprises the novel products as well as the novelprocesses and steps of processes according to which such products aremanufactured, the specific embodiments of which are describedhereinafter by way of example and in accordance with which we now preferto practice the invention.

We have found in accordance with our invention that the heat instabilityof such ester plastieizersis due primarily to the presence in the esterof dialkyl sulfate orsimilar alkyl compound with a strong acid radical,which decomposes at high temperature, such asemployed in molding, toliberate sulfuric acid. The acid then decomposes the ester giving acidand colored products. The acid products tend to deteriorate the resinand the colors produced, particularly dark colors, are usuallyobjectionable.

In accordance with our invention, we heat a mixture of an estercontaining an impurity having a-strong acid radical in sutficientquantity to cause discoloration in heating of the ester, with an agentto render the liberated The impurity is, as pointed out ing which theheating, in

2,805,246 Patented Sept. 3, 1957 a strong acid radical. This acid :is.sufiicientzto cause deterioration and discoloration of many syntheticresins when heated therewith. The agent .for rendering the.impurityinactive is preferably an aqueous saltlof .a weak acid, but may consistof other materials as discussed below. After treatment with ,the agent,the later with the inactivated impurity is separated from .theester.

The heat treatment of the ester according to this inventionisvpreferably performed either in the presence of .an aqueous solution ofasoluble salt of a weak .acid, such as aqueous sodium carbonate, or analkaline hydroxide, or in the presence of a dry salt of a weak acid,such as sodium carbonate, or else in the presence of water, :only. Bytheuse ofsuch salt or hydroxide, the sulfuric acid is neutralized as itis formed and may be removed. Where "ice only water is used, thesulfuric acid as it is formed is dissolved by the water so that itsstrength becomes low enough to render it unable to attack the ester,then the aqueous acid is separated by decantation and the ester isfinally neutralized :to eliminate-any traces of acid.

It is necessary to provide, during the treatment, an intimate contact-ofthe ester with the water or the neutralizing solution, this beingaccomplished byrneans of a stirrer, a pump or any other adequate means.

The minimum duration of the heat treatment depends upon the kind ofester treated and the temperature of treatment.

Thus, for example, octyl phthalate shoudl be subjected to the .heattreatment for at least 165 minutes at C., or 90 minutes at or 60 minutesat C.

The product thus treated, afterseparation from water, washing forremoval therefrom of dissolved neutralizing substance, then drying, maylater on be heated to a high temperature without developing color noracidity.

The process of this invention-maybe applied generally to any and allplasticizers produced by esterification of an alcohol, glycol or polyolwith an acid or acid anhydride, for example butyl, octyl or nonylphathalates or adipates, triethylene glycol dihexanoic ester, and thelike.

.For each ester plasticizer the optimum conditions of time andtemperature to be applied may be difierent,-but it may be said generallythat the temperature should be ch sen within the ang o 0=3 80 C- andtheit me du com-.natinn with th other means disclosed, is applied :may'ie of irom 30 minutes to 5 hours.

The heat treatment may be applied either to the finishedester, that is,after separation therefrom of excess alcohol, water entrainer if any andcatalyst employed by the esterification reaction, or to the ester at astage of its production (more particularly, immediately after theesterification reaction), in the presence of water entrainer, if any,water, catalyst and excess alcohol or acid;

plication diagrammatically show'two devices which may be employed tocarry out this invention.

In the case of Fig. 1, the heat treatment zone consists of a pipe 1,part of which constitutes one of the elements of a heat exchanger, theother element of which is a heating pipe 2 through which steam flows asshown by the arrows. Pipe 1 belongs to a circuit including a pump 3causing .high speed circulation and turbulence .of the mixture of esterto be treated, introducedthrough pipe 4,

e 3 and treatment agent, introduced through pipe 5 just upstream of apump 6 which feeds the circuit.

After leaving the circuit at a rate corresponding to the feed, thereaction mixture passes through a cooler 7, then flows to a decanter 8where the ester is separated from the treatment agent. The ester iswithdrawn through pipe 9, and the agent through pipe 10.

The apparatus of Fig. 2 differs from that of Fig. 1 in that the circuit,1-3, is replaced by a tower 11 containing filling material and envelopedby a heating jacket 12.

In continuous operation, for a given temperature the time of sojourn inthe apparatus will vary according to the mode of operation and will bedetermined, for each particular case, by applying the general formulaeof chemical kinetics.

The preferred conditions for the carrying out of this invention are thetreatment of the raw product of the esterification reaction and the useof a sodium carbonate aqueous solution as a treatment agent. Thisaqueous solution causes direct neutralization of the esterificationcatalyst, whereas if water only is used for treating the rawesterification mixture, subsequent neutralization of the catalystdissolved in the water is also necessary. As said above, it is possibleto use sodium hydroxide or other caustic alkali, but the operation isdelicate because of the risk, under certain conditions, of causingpartial saponification of the ester plasticizer treated. That is 7 whythe use of sodium carbonate is preferred.

Before giving examples illustrating this invention, we describe belowthe three tests referred to in the following examples.

1.-Acidity test-Acidity in millimolecules per liter of the esterplasticizer is determined before and after a two-hours heating at 160 C.

2.Col0r test-Color is determined by means of Lovibond tintometer with a6-inch cell, before and after a 15-minutes heating at 180 C.

3.Paper test.A filter paper hour in a sample of the ester heated at 180C., then the color of the paper is determined by means of the Lovibondtintometer, by reflection.

Example 1 500 milliliters of octyl phthalate having the followingcharacteristics:

Acidity test: before heating, 0.27; after heating, 3.5

is immersed for one Color test: before heating, 0.4 Yellow+0.1 Red;after heating, 4.9 Yellow-l-Ll Red Paper test: 8.5 Yellow+7 Red+9 Bluetion, washed with warm water and dried by passing warm air therethrough.After treatment, its characteristics were as follows:

Acidity test: before heating, 0.2; after heating, 0.8

Color test: before heating, 0.4 Y+0.1 R; after heating,

Paper test: 0.6 Y+0.3 R

Example 2 500 milliliters of the same octyl phthalate as in Example 1were heated for 90 minutes at 160 C., under stirring, with millilitersof normal aqueous sodium hydroxide. After water washing and drying, thecharacteristics were as follows: Acidity test: before heating, 0.14after heating, 0.75

Color test: before heating, 0.4 Y+0.1 R; after heating,

Paper test: 0.8 Y+0.5 R

It was found that 3.5% by weight of the octyl phthalate treated was saponified.

Example 3 The same mixture as in Example 1 was heated for one hour atC., under stirring. After water washing and drying, the characteristicsof the ester were as follows:

Acidity test: before heating, 0.12; after heating, 0.8

Color test: before heating, 0.5 Y+0.1 R; after heating,

Paper test: 0.6 Y+0.3 R

Example 4 Octyl phthalate to be stabilized had the followingcharacteristics:

Acidity test: before heating, 0.25; after heating, 5

Color test: before heating, 1.7 Y+0.6 R; after heating,

Paper test: black Acidity test: before heating, 0.2; after heating, 2.2

Color test: before heating, 1.4 Y +0.1 R; after heating,

Paper test: 0.8 Y+0.3 R

Example 5 At the exit point of a continuous esterification apparatusthere was obtained a mixture containing, by weight, 86% octyl phthalate,13% octyl alcohol and 1% benzene. 360 liters per hour of this mixture,together with 70 liters per hour of 15% aqueous solution of sodiumcarbonate, were introduced into a treatment circuit' of 1430 literscapacity, maintained at C. The phthalate leaving the circuit wasdecanted, washed with warm water, steam-distilled in a distillationcolumn for removal of the alcohol and the benzene, and finally driedwith warm air in a tower filled with Raschig rings. The so-treatedphthalate showed a paper test of 0.6 Y+0.2 R, while if the heating stepat 175 C. be omitted, the paper test was 6 Y+3 R.

Example The starting material was octyl adipate produced from adipicacid and excess octyl alcohol in the presence of sulfuric acid. Thecharacteristics of the ester were as follows:

Acidity test: before heating, 0.6; after heating, 5.1.

Color test: before heating, 21 Y+4.2 R; after heating,

Paper test: black The ester was heated for 30 minutes at 170 C. with anequal volume of water, then neutralized with sodium carbonate, washedand dried. The characteristics of the treated ester were as follows:

Acidity test: before heating, 0.15; after heating, 1.75

Color test: before heating, 15 Y+2.4 R; after heating,

Paper test: 6 Y+3 R Should the heat treatment time be one hour insteadof 30 minutes, the characteristics of the ester would become as follows:

Acidity test: before heating, 0.15; after heating, 1.25

Color test: before heating, 10 Y+2 R; after heating,

Paper test: 2 Y+0.5 R

Example 7 The starting material was the raw product of esterification ofphthalic anhydride by butyl alcohol, containing 80% by weight of butylphthalate and 20% by weight of butyl alcohol, and containing in additionthe acid esterification catalyst.

If this raw product was only neutralized cold by stirring for 10 minutes500 ml. thereof with 100 ml. of 10% aqueous solution of sodiumhydroxide, then decanted, washed, separated from the excess alcohol anddried, the characteristics of the ester would be the following:

Acidity test: before heating, 0.15; after heating, 4.5

Color test: before heating, 0.7 Y+0.2 R; after heating,

Paper test: black On the other hand, if, in accordance with thisinvention, 500 ml. of the raw product are heated for 4 hours at 80 C.with 100 ml. of 10% aqueous solution of sodium carbonate, thecharacteristics become as follows:

Acidity test: before heating, 0.1; after heating, 2

Color test: before heating, 0.6 Y+0.3 R; after heating,

Paper test: 1.4 Y+0.6 R

If the heating step is carried out for one hour at 130 C., thecharacteristics are as follows:

Acidity test: before heating, 0.15; after heating, 1.5

Color test: before heating, 0.3 Y+0.1 R; after heating,

Paper test: 1 Y+0.2 R

Example 8 Triethylene glycol di-2:ethylhexanoic ester to be stabilizedhad the following characteristics:

Acidity test: before heating, 5; after heating, 12

Color test: before heating, 6 Y+1.1 R; after heating,

11 Y+2.l R

Paper test: black 500 ml. of this ester were heated for one hour at 130C., under stirring, with 100 ml. of aqueous solution of sodiumcarbonate. After water washing and drying, the characteristics were asfollows:

Acidity test: before heating, 2; after heating, 6

Color test: before heating, 2 Y+0.3 R; after heating,

Paper test: 0.6 Y+0.2 R

Another sample of 500 m1. of the same starting ester was subjected tothe same treatment, but at a temperature of 115 C. for 80 minutes. Thecharacteristics of the final product were as follows:

Acidity test: before heating, 1.6; after heating, 4.75

Color test: before heating, 1.4 Y+0.2 R; after heating,

Paper test: 0.5 Y+0.2 R

We claim:

1. A process which comprises heating a plasticizer ester containing acatalyst-acid-ester-impurity with an aqueous solvent at about 180 C. forabout 30 minutes- 5 hours, whereby the impurity is inactivated withoutsubstantial decomposition of the plasticizer ester, and separating theplasticizer ester from said impurity.

2. A process which comprises continuously flowing in a zone a mixture ofa plasticizer ester containing a catalyst-acid-ester-impurity and anaqueous solvent, heating the mixture to about 70180 C. for about 30minutes- 5 hours, whereby the impurity is inactivated withoutsubstantial decomposition of the plasticizer ester, and continuouslyseparating the plasticizer ester from the impurity.

3. A process which comprises heating octylphthalate containing acatalyst-acid-ester-impurity with an aqueous solution of sodiumcarbonate at about 70-l80 C. for about 30 minutes-Shours, whereby theimpurity is inactivated without substantial decomposition of saidoctylphthalate, and separating the octylphthalate from the impurity.

References Cited in the file of this patent UNITED STATES PATENTS1,993,737 Graves et al. Mar. 12, 1935 2,147,488 Hickman et al. Feb. 14,1939 2,494,133 Jetfs Ian. 10, 1950 2,653,165 Levine Sept. 22, 19532,699,434 Turck Jamil, 1955

1. A PROCESS WHICH COMPRISES HEATING A PLASTICIZER ESTER CONTAINING ACATALYST-ACID-ESTER-IMPURITY WITH AN AQUEOUS SOLVENT AT ABOUT 70-180*C.FOR ABOUT 30 MINUTES5 HOURS, WHEREBY THE IMPURITY IS INACTIVATED WITHOUTSUBSTANTIAL DECOMPOSITION OF THE PLASTICIZER ESTER, AND SEPARATING THEPLASTICIZER ESTER FROM SAID IMPURITY.